Water And Fertilizer Treatment Controls Heavy Metal Pb Pollution In Soil In Sewage Irrigation Areas

Due to the combined influence of natural factors and human factors,heavy metal pollution in cultivated land in my country is increasing.Heavy metal-contaminated soil not only has a coercive effect on the growth of crops,but also causes the concentration of heavy metals in agricultural products to exceed the standard,which seriously damages human health.Based on this,this study selected the sewage irrigation area in the northern suburbs of Xi’an as the research area,measured and analyzed the total amount and form of heavy metals in the farmland soil,and screened and studied the heavy metal Pb in the soil.And tried to study the transformation process of heavy metal Pb forms in soil under different water and fertilizer treatment conditions by controlling soil water content and potassium fertilizer application rate,in order to provide information on the change trend of the exchangeable state of Pb in soil and its impact on bioavailability and then provide a certain reference for the remediation of heavy metal Pb pollution in soil in sewage irrigation areas in the future.The main findings were as follows:（1）Pb dominated and was obviously enriched in soil heavy metal elements in the sewage irrigation area of the northern suburbs of Xi’an,which all exceed the soil background value and Pb standard limit in Xi’an,and the proportion of exchangeable and carbonate-bound Pb was between 58.18%-74.39%and accounted for a large proportion.（2）The change of soil physical and chemical properties affected the occurrence form of heavy metals in soil.The exchangeable state of heavy metals had a significant negative correlation with water content,and a significant positive correlation with total potassium.The change of water content and total potassium significantly affected the exchangeable state of heavy metals.（3）The content of exchangeable Pb in soil under different water and fertilizer treatments showed a decreasing trend and the decline range was between 138.90-263.73mg/kg;the carbonate-bound Pb content in the soil increased first and then gradually decreased;the iron-manganese oxide-bound Pb content showed an increasing trend,and the increase range was between 97.77-193.73 mg/kg;the content of organically bound Pb in the soil shows an upward trend with the increase of cultivation time,but the upward trend was not obvious;the residual Pb content in the soil had little difference at the beginning,and then gradually increased and the increase range was 42.73-74.82 mg/kg.With the increase of culture time,the proportion of exchanged and carbonate-bound Pb continued to decrease,while the proportion of iron and manganese oxide bound state,organic bound state and residual Pb continued to increase.Among the water and fertilizer control measures,the water and fertilizer treatment conditions of 60%field capacity and 0.3 g/kg K₂SO₄ were the optimal combination,that is,the soil heavy metal Pb activity under the water and fertilizer treatment were the lowest.（4）Soil p H gradually increased with the increase of cultivation time under different water and fertilizer treatments,and when the soil is slightly alkaline,the increase of p H is conducive to the transformation of exchangeable and carbonate-bound Pb to the existing forms of several other heavy metals.In general,soil organic matter increased slowly at first and then remained stable with the increase of culture time.The increase of organic matter was conducive to the transformation of exchangeable Pb to other existing forms.